Book Cipher
Encode words as reference positions or decode positions with the same passage.
How Book Cipher works
Book Cipher handles message words into one-based positions from a user-supplied reference passage, using the first case-insensitive occurrence of each word. The passage and message are tokenized into Unicode words. Encoding looks up first positions and marks absent words; decoding replaces valid numeric positions with reference tokens. The Book Cipher exposes its message or positions, reference passage, operation controls so this particular convention stays inspectable instead of hiding behind an unexplained preset.
With the default sentence as the book, the moon rises becomes 2 6 7 because those words first appear at those positions. Puzzle makers can build reproducible word-index clues without relying on a copyrighted or external book that other visitors may not possess. The Book Cipher presents a deterministic plain-text result that can be copied and compared with the worked value before it enters another workflow.
Limits and private processing
Repeated reference words always use their first position, punctuation is ignored, and both parties need identical reference wording. This simple form is easy to analyze. The Book Cipher performs its complete operation locally in your browser; neither the source text nor its settings are uploaded, stored remotely, or sent through an external request.
Frequently Asked Questions
How does the Book Cipher work?
The passage and message are tokenized into Unicode words. Encoding looks up first positions and marks absent words; decoding replaces valid numeric positions with reference tokens.
What does the default Book Cipher example return?
With the default sentence as the book, the moon rises becomes 2 6 7 because those words first appear at those positions.
What limitation should I know about?
Repeated reference words always use their first position, punctuation is ignored, and both parties need identical reference wording. This simple form is easy to analyze.
Is the Book Cipher private?
Yes. This specific book cipher operation runs locally in your browser and does not transmit the input or settings.
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